This past weekend was this first time using it. I sure hope it wont cost me 100.00 a month. I'm in Florida so I hope after a few weeks I wont have to use it at all. I do know it only took 4 to 5 hours on Saturday to warm up my 12,400 gal pool and the next day (Sunday) when I turned it back on it took maybe only one hour. (May I ask who is your Pool Builder?)